After scaling the values down, interesting things tend to happen in
the darkgrey region. Thus, split it into three parts: dark grey,
light grey and yellow (warning). This makes the colours inconsistent
with the status light, though -- ideas welcome.

As going into actual harmful contamination still isn't as bad as for
other races, thus this commit has the gauge's limit calibrated at
8000 rather than 5000. We could put it farther, but then, it would
end up as your typical car gauge where on some models if you get to
halfway of the scale, there's a police chase after you.